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package com.oracle.truffle.jx.runtime;

import com.oracle.truffle.api.*;
import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
import com.oracle.truffle.api.dsl.Cached;
import com.oracle.truffle.api.dsl.Fallback;
import com.oracle.truffle.api.dsl.ReportPolymorphism;
import com.oracle.truffle.api.dsl.Specialization;
import com.oracle.truffle.api.interop.InteropLibrary;
import com.oracle.truffle.api.interop.TruffleObject;
import com.oracle.truffle.api.library.ExportLibrary;
import com.oracle.truffle.api.library.ExportMessage;
import com.oracle.truffle.api.nodes.DirectCallNode;
import com.oracle.truffle.api.nodes.IndirectCallNode;
import com.oracle.truffle.api.source.SourceSection;
import com.oracle.truffle.api.strings.TruffleString;
import com.oracle.truffle.api.utilities.CyclicAssumption;
import com.oracle.truffle.api.utilities.TriState;
import com.oracle.truffle.jx.JanivaLang;
import com.oracle.truffle.jx.nodes.JXUndefinedFunctionRootNode;
import java.util.logging.Level;

/**
 * Represents a SL function. On the Truffle level, a callable element is represented by a {@link
 * RootCallTarget call target}. This class encapsulates a call target, and adds version support:
 * functions in SL can be redefined, i.e. changed at run time. When a function is redefined, the
 * call target managed by this function object is changed (and {@link #callTarget} is therefore not
 * a final field).
 *
 * <p>Function redefinition is expected to be rare, therefore optimized call nodes want to speculate
 * that the call target is stable. This is possible with the help of a Truffle {@link Assumption}: a
 * call node can keep the call target returned by {@link #getCallTarget()} cached until the
 * assumption returned by {@link #getCallTargetStable()} is valid.
 *
 * <p>The {@link #callTarget} can be {@code null}. To ensure that only one {@link JXFunction}
 * instance per name exists, the {@link JXFunctionRegistry} creates an instance also when performing
 * name lookup. A function that has been looked up, i.e., used, but not defined, has a call target
 * that encapsulates a {@link JXUndefinedFunctionRootNode}.
 */
@ExportLibrary(InteropLibrary.class)
@SuppressWarnings("static-method")
public final class JXFunction implements TruffleObject {

  public static final int INLINE_CACHE_SIZE = 2;

  private static final TruffleLogger LOG = TruffleLogger.getLogger(JanivaLang.ID, JXFunction.class);

  /** The name of the function. */
  private final TruffleString name;

  /** The current implementation of this function. */
  private RootCallTarget callTarget;

  /**
   * Manages the assumption that the {@link #callTarget} is stable. We use the utility class {@link
   * CyclicAssumption}, which automatically creates a new {@link Assumption} when the old one gets
   * invalidated.
   */
  private final CyclicAssumption callTargetStable;

  protected JXFunction(JanivaLang language, TruffleString name) {
    this(name, language.getOrCreateUndefinedFunction(name));
  }

  protected JXFunction(TruffleString name, RootCallTarget callTarget) {
    this.name = name;
    this.callTargetStable = new CyclicAssumption(name.toJavaStringUncached());
    setCallTarget(callTarget);
  }

  public TruffleString getName() {
    return name;
  }

  protected void setCallTarget(RootCallTarget callTarget) {
    boolean wasNull = this.callTarget == null;
    this.callTarget = callTarget;
    /*
     * We have a new call target. Invalidate all code that speculated that the old call target
     * was stable.
     */
    LOG.log(Level.FINE, "Installed call target for: {0}", name);
    if (!wasNull) {
      callTargetStable.invalidate();
    }
  }

  public RootCallTarget getCallTarget() {
    return callTarget;
  }

  public Assumption getCallTargetStable() {
    return callTargetStable.getAssumption();
  }

  /**
   * This method is, e.g., called when using a function literal in a string concatenation. So
   * changing it has an effect on SL programs.
   */
  @Override
  public String toString() {
    return name.toJavaStringUncached();
  }

  @ExportMessage
  boolean hasLanguage() {
    return true;
  }

  @ExportMessage
  Class<? extends TruffleLanguage<?>> getLanguage() {
    return JanivaLang.class;
  }

  /** {@link JXFunction} instances are always visible as executable to other languages. */
  @SuppressWarnings("static-method")
  @ExportMessage
  @TruffleBoundary
  SourceSection getSourceLocation() {
    return getCallTarget().getRootNode().getSourceSection();
  }

  @SuppressWarnings("static-method")
  @ExportMessage
  boolean hasSourceLocation() {
    return true;
  }

  /** {@link JXFunction} instances are always visible as executable to other languages. */
  @ExportMessage
  boolean isExecutable() {
    return true;
  }

  @ExportMessage
  boolean hasMetaObject() {
    return true;
  }

  @ExportMessage
  Object getMetaObject() {
    return JXType.FUNCTION;
  }

  @ExportMessage
  @SuppressWarnings("unused")
  static final class IsIdenticalOrUndefined {
    @Specialization
    static TriState doSLFunction(JXFunction receiver, JXFunction other) {
      /*
       * SLFunctions are potentially identical to other SLFunctions.
       */
      return receiver == other ? TriState.TRUE : TriState.FALSE;
    }

    @Fallback
    static TriState doOther(JXFunction receiver, Object other) {
      return TriState.UNDEFINED;
    }
  }

  @ExportMessage
  @TruffleBoundary
  static int identityHashCode(JXFunction receiver) {
    return System.identityHashCode(receiver);
  }

  @ExportMessage
  Object toDisplayString(@SuppressWarnings("unused") boolean allowSideEffects) {
    return name;
  }

  /**
   * We allow languages to execute this function. We implement the interop execute message that
   * forwards to a function dispatch.
   *
   * <p>Since invocations are potentially expensive (result in an indirect call, which is expensive
   * by itself but also limits function inlining which can hinder other optimisations) if the node
   * turns megamorphic (i.e. cache limit is exceeded) we annotate it with {@ReportPolymorphism}.
   * This ensures that the runtime is notified when this node turns polymorphic. This, in turn, may,
   * under certain conditions, cause the runtime to attempt to make node monomorphic again by
   * duplicating the entire AST containing that node and specialising it for a particular call site.
   */
  @ReportPolymorphism
  @ExportMessage
  abstract static class Execute {

    /**
     * Inline cached specialization of the dispatch.
     *
     * <p>Since SL is a quite simple language, the benefit of the inline cache seems small: after
     * checking that the actual function to be executed is the same as the cachedFuntion, we can
     * safely execute the cached call target. You can reasonably argue that caching the call target
     * is overkill, since we could just retrieve it via {@code function.getCallTarget()}. However,
     * caching the call target and using a {@link DirectCallNode} allows Truffle to perform method
     * inlining. In addition, in a more complex language the lookup of the call target is usually
     * much more complicated than in SL.
     *
     * <p>{@code limit = "INLINE_CACHE_SIZE"} Specifies the limit number of inline cache
     * specialization instantiations.
     *
     * <p>{@code guards = "function.getCallTarget() == cachedTarget"} The inline cache check. Note
     * that cachedTarget is a final field so that the compiler can optimize the check.
     *
     * <p>{@code assumptions = "callTargetStable"} Support for function redefinition: When a
     * function is redefined, the call target maintained by the SLFunction object is changed. To
     * avoid a check for that, we use an Assumption that is invalidated by the SLFunction when the
     * change is performed. Since checking an assumption is a no-op in compiled code, the assumption
     * check performed by the DSL does not add any overhead during optimized execution.
     *
     * @see Cached
     * @see Specialization
     * @param function the dynamically provided function
     * @param arguments the arguments to the function
     * @param callTargetStable The assumption object assuming the function was not redefined.
     * @param cachedTarget The call target we aim to invoke
     * @param callNode the {@link DirectCallNode} specifically created for the {@link CallTarget} in
     *     cachedFunction.
     */
    @Specialization(
        limit = "INLINE_CACHE_SIZE", //
        guards = "function.getCallTarget() == cachedTarget", //
        assumptions = "callTargetStable")
    @SuppressWarnings("unused")
    protected static Object doDirect(
        JXFunction function,
        Object[] arguments,
        @Cached("function.getCallTargetStable()") Assumption callTargetStable,
        @Cached("function.getCallTarget()") RootCallTarget cachedTarget,
        @Cached("create(cachedTarget)") DirectCallNode callNode) {

      /* Inline cache hit, we are safe to execute the cached call target. */
      Object returnValue = callNode.call(arguments);
      return returnValue;
    }

    /**
     * Slow-path code for a call, used when the polymorphic inline cache exceeded its maximum size
     * specified in <code>INLINE_CACHE_SIZE</code>. Such calls are not optimized any further, e.g.,
     * no method inlining is performed.
     */
    @Specialization(replaces = "doDirect")
    protected static Object doIndirect(
        JXFunction function, Object[] arguments, @Cached IndirectCallNode callNode) {
      /*
       * SL has a quite simple call lookup: just ask the function for the current call target,
       * and call it.
       */
      return callNode.call(function.getCallTarget(), arguments);
    }
  }
}
